The present invention generally relates to lead-acid storage batteries and, more particularly, to a woven-grid, sealed, quasi-bipolar lead-acid battery construction and fabricating method.
A conventional bipolar battery generally includes electrodes having a metallic substrate on which positive active material forms one surface and negative active material forms the opposite surface. The active materials are retained by various means on the metal conductive substrate which is impermeable to electrolyte ions. The electrodes are arranged in parallel, stacked relation to provide a multicell battery with electrolyte and separator plates providing an interface between adjacent electrodes. Conventional monopolar electrodes, used at the ends of the stack are electrically connected with the output terminals. While achieving respectable power densities, these conventional bipolar battery designs suffer substrate corrosion, seal and active material retention problems. For these reasons, bipolar versions of the standard lead-acid battery have failed to gain commercial success.
Two recent battery constructions have been proposed which avoid many disadvantages of prior bipolar battery constructions. One construction is the improved lightweight bipolar battery disclosed in U.S. Pat. No. 4,275,130 to Rippel et al and assigned to the assignee herein. The improved bipolar battery construction has a plurality of spaced thin biplates each being of composite thermoplastic material with conductive fibers such as carbon, graphite or metallic fibers serving as strengthening and conductive elements. Also, each biplate has spaced lead stripes on opposite side surfaces in bonded electrical contact with the graphite fibers, with nonstriped areas being provided with protective coating. A plurality of thin separator plates of thermoplastic material are interleaved with the biplates, each separator plate having bonded thereto porous resiliently yieldable mats serving to carry active material. Each biplate is bonded to a casing member which, in turn, is bonded to adjacent casing members. The interleaved biplates and separator plates are held in a stack under compression and maintained in operable assembly with the active material in contact with the lead stripes by external pressure means.
The other construction is the improved light-weight quasi-bipolar battery disclosed in U.S. Pat. No. 4,353,969 to Rippel et al and assigned to the assignee herein. (The term "quasi-bipolar" is used to mean that the biplate structure of this construction, unlike in most prior bipolar battery constructions, does not conduct electrical current through the material of the biplate structure.) The improved quasi-bipolar battery of the cited patent employs a frameless, flexible biplate construction. It utilizes a continuous strip of thermoplastic material folded into pleated biplate walls and sealed along longitudinal edge portions thereof to provide sealed chambers adapted to receive separator plates and to contain electrolyte liquid. The continuous thermoplastic strip serves not only to provide the biplate structures but also the battery casing structure. Each separator plate includes a scrim fabric means for holding active material and attached by bonding to a porous mat carried by a micro-porous separator substrate. The scrim fabric means and porous mats contain electrolyte liquid. The top opening of each chamber can be covered and sealed by a top seal member of thermoplastic material bonded to the biplate structure.
These two recent battery constructions of the above-cited patents avoid many of the disadvantages of prior bipolar battery constructions, such as excess weight, sealing and corrosion problems, off gassing, limited energy and power densities and reduced cycling life. Further, these constructions are useful for virtually all battery applications and particularly for electrical vehicles in which the ratio of energy and power to battery weight is critical for the distance range, speed, and acceleration of the electrical vehicle.
Notwithstanding the advantages and benefits believed to be achieved by the above-described recent battery constructions, a need continues for a quasi-bipolar, lead-acid battery construction having improved weight-to-power ratio, maintenance free operation, high specific energy, vibration and g-force resistance, long life expectancy and many other design parameter improvements.